Freeform Diffractive Optical Element for VCSEL Transmitter Noise Reduction
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Solution Overview
Problem
Current optical coupling systems in high-speed data communications networks face challenges in controlling launch conditions and noise reduction due to limitations in manufacturability, particularly with multimode optical fibers, leading to issues like back reflection, relative intensity noise, mode partitioning noise, and mode selective noise, which are not adequately addressed by existing glass DOEs when replicated in plastic.
Innovation Solution
A freeform diffractive optical element (DOE) is designed using computer-generated holograms, transformed to be compatible with low-cost fabrication processes like injection molding, allowing for mass production of plastic DOEs that achieve similar functionality to glass DOEs, thereby reducing noise and improving launch conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If glass DOEs are used to control launch conditions and reduce noise, then noise reduction performance is improved, but manufacturing cost and complexity increase
Solution Approach 1:
The patent replaces expensive glass DOEs with inexpensive plastic DOEs that can be mass-produced through injection molding. The plastic material allows for cost-effective manufacturing while maintaining the necessary optical functionality to reduce noise in VCSEL-based optical communication systems.
Solution Approach 2:
The patent transforms the DOE surface profile from a discrete multi-level CGH structure to a continuous smooth profile through mathematical transformation. This parameter change enables compatibility with injection molding processes while preserving the optical phase modulation capability needed for noise reduction.
2Manufacturing precision
If discrete multi-level CGH DOE design is used, then optical phase control precision is improved, but manufacturability deteriorates
Solution Approach 1:
The patent applies a mathematical transformation that converts the discrete multi-level surface profile into a continuous smooth curved profile. This transformation maintains the optical phase control functionality while creating a surface geometry that is compatible with injection molding processes, thereby improving manufacturability.
Solution Approach 2:
The patent creates a transformed DOE design that copies the essential optical functionality of the original discrete CGH DOE but adapts it to a continuous profile suitable for mass production through injection molding, enabling replication of the noise reduction effect at lower cost.
3Ease of operation
If imaging-type optical coupling system is used, then launch condition control is improved, but device complexity increases
Solution Approach 1:
The patent extracts the launch condition control functionality from a complex multi-element imaging optical coupling system and concentrates it into a single transformed DOE. This simplifies the overall system by eliminating the need for multiple optical elements while maintaining effective launch condition control for noise reduction.
Solution Approach 2:
The transformed DOE performs multiple functions simultaneously: it controls launch conditions, reduces back reflection, and minimizes various noise types (RIN, MPN, MSN) in a single optical element, thereby reducing overall system complexity while maintaining comprehensive noise reduction capability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The transformed plastic DOEs effectively reduce back reflection, relative intensity noise, mode partitioning noise, and mode selective noise, achieving performance comparable to glass DOEs while enabling low-cost, high-quality mass production.
Implementation Method 1
a diffractive element... The freeform DOE provides the desired launch control over the laser light
Implementation Method 2
DOEs created using computer generated holograms (CGHs) can also be used to suppress optical feedback
Data Source
AI summary
A freeform DOE for use in an optical transmitter and a method of designing and manufacturing the DOE are provided. The freeform DOE is capable of achieving the same, or nearly the same, functionality as that of a glass DOE, but has a design that has been transformed to make the surface profile of the DOE compatible with a molding process that can be used to manufacture the DOE with high quality at low costs. The method of designing and manufacturing the DOE includes preselecting a CGH that will obtain a target freeform DOE design, using a preselected smoothing function to smooth the surface profile of the target freeform DOE design to transform the design into a DOE design that is compatible with a molding process, and using a fabrication process to manufacture a freeform DOE that is based on the transformed DOE design.